Stovepipe Power: Using Waste Heat

If you've been thinking about ways of using waste heat from you cookstove rather than letting it escape, here are a number of suggested stovepipe modifications to make it possible.

By A. Michael Wassil

| November/December 1973

FIG 1: In a single-storied structure, put the stove at one end of the building and carry the pipe horizontally to the other end and then out. FIG 2: In a structure with two or more stories, run the vent straight up through the rooms above.

ILLUSTRATION: MOTHER EARTH NEWS STAFF

With all the discussion that's going on about natural power
for home use, no one yet seems to have expounded at length
on one source of energy that's readily available to
homesteaders: namely, the heat that goes up the old
stovepipe. Seems a shame to let those calories get away ...
especially when you think of them in terms of firewood and
all the energy you've expended cutting it.

Although I've
never actually measured the B.t.u.'s roaring out the top
end of a stovepipe, I have toasted bread (in about one
second) and boiled pots of water in the hot blast from a
small stove. Perhaps some thermal buff out there in
MOTHER EARTH NEWSland would like to do the measurements on the
quantity of heat that escapes up the flue . . . given
various-sized stoves, different lengths and diameters of
stovepipe and varying intensities of flame in the firebox. At any rate, while the rest of us are waiting for such a
report, here are a few suggestions for utilizing some of
that energy.

[1] Use the stovepipe itself as a radiant
heater, the way many pioneer builders did in New England,
here in Ontario, and elsewhere. In a single-storied
structure, put the stove at one end of the building and
carry the pipe horizontally to the other end and then out. When there's more than one story, just
run the vent straight up through the rooms above. Whatever you do, though, don't run your stovepipe up two feet and then outside.

[2] The
Palace Grand in Dawson City, Yukon Territory has a unique
(the owners claim) variation on Suggestion Number 1. Their
device—which they call a double stove—is simply
a large hot air chamber part way up the stovepipe that
traps some of the escaping heat and radiates it into the
room.

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FIG 1: In a single-storied structure, put the stove at one end of the building and carry the pipe horizontally to the other end and then out. FIG 2: In a structure with two or more stories, run the vent straight up through the rooms above.ILLUSTRATION: MOTHER EARTH NEWS STAFF

FIG 3: The Palace Grand in Dawson City, Yukon Territory developed a drum-within-a-drum design to create a large hot air chamber that traps stovepipe heat and radiates it into the room. FIG 4: An unmodified 45 gallon steel drum could possibly serve the same purpose. MOTHER EARTH NEWS STAFF

FIG 5: It involves a little plumbing, but the stovepipe could be routed through a 45 gallon drum fitted with a water inlet at the top and a spigot at the bottom, creating a water heater, radiator, and hot water supply all in one.MOTHER EARTH NEWS STAFF

FIG 6: A stovepipe fitted with an oven. You could buy one, or make one from a 45 gallon drum and Yukon can.MOTHER EARTH NEWS STAFF

FIG 7: A proposed concentric double stovepipe in which the inner pipe is an intake drawing exterior air and the outer is an exhaust pipe that warms the inflow. FIG: At the stove end of a concentric pipe design, the intake should be routed through the bottom of the firebox into the ash box chamber.MOTHER EARTH NEWS STAFF

The model in Dawson is a bit complicated, and
consists of a modified 45-gallon steel drum. I
imagine that an unmodified steel drum would also
work. Either version would be more efficient filled with
pebbles or stones, which would absorb
heat—sauna-style—and radiate it back even after
the stove itself had burned low. Don't pack in the rocks
very snugly, though, or you'll kill the draft.

[3] Instead
of an air chamber, put a water tank on the
stovepipe. This involves a little plumbing since you have
to run the pipe through the middle of the water container.
You'll need a tap at the bottom of the tank and some sort
of inlet at the top (this could be as elaborate as a float
valve hooked up to your main water source to keep the
reservoir full automatically, or as simple as a movable lid
that allows you to dump in replacement water by hand).
There you are ... a convenient hot water supply.

Although
insulation will keep the water in the tank hot longer, I'd
advise against it. In the winter, when the stove is going all the time, the
water will never get cool anyhow ... and the bare metal of
the reservoir will act as a radiator.

[4] Put an oven in the stovepipe. Units that fit into a standard smoke
vent used to be available commercially (and as far as /
know they still are ... from the Louisville Tin and Stove
Company—MOTHER EARTH NEWS). Or you can make your own.

[5] In
MOTHER EARTH NEWS, Bill Lange suggested a concentric
double stovepipe in which one of the conduits draws outside
air into the heater and warms it in the process.

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I suggest using the center pipe as the intake and extending
it a couple of feet higher at the upper end than the
surrounding output duct. At the lower—or
stove—end, the intake pipe should be taken right through
the bottom of the firebox into the ash box chamber.

This arrangement, of course, would necessitate some
modification of the damper so, instead, you could run the
intake pipe around the damper ... or eliminate the damper
itself and regulate the firebox by a smaller valve in the
intake pipe only.

[6] Finally, and most elaborately of all,
you could use that stovepipe heat to boil water to run a
small steam engine, either a conventional piston type or a
more efficient turbine. The steam engine in turn could
power a small generator to supply a modest amount of
electricity ... sufficient, maybe, to operate a few light
bulbs.

As a matter of fact, I'm planning a stovepipe-powered
turbine myself and would like to enlist the help of
MOTHER EARTH NEWS' readers. Can anyone out there tell me how much
current is needed to operate two or three small fluorescent
bulbs, how small a generator would suffice to provide that
current, and how much power a steam engine would have to
develop to run such a generator?

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